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Aerosol Transport – Inertia


:: Section 8

Curvilinear Motion and Stokes Number

  Section Contents
II. Stokes Number

Curvilinear motion is characterized by a dimensionless number called the Stokes number (Stk). It is the ratio of the stopping distance of a particle to a characteristic dimension of the obstacle. For example, for a flow of diameter dc making a 90° turn, perpendicular to a cylinder the Stokes number is

where U is the flow velocity, for Rep < 1.0.

When Stk >> 1, particles continue moving in a straight line when the gas turns; when Stk << 1, particles follow the gas streamlines perfectly and make the turn. So Stokes number is the ratio of a particle's "persistence" to the size of the obstacle and it is used to characterize inertial impaction, which is described in the next section.


How to increase Stk?